This invention relates to a carburetor for a combustion engine and more particularly to a carburetor having a priming pump with an integral fuel bowl drain.
Carburetors, especially those found on small engines such as garden equipment, small outboard motors and utility engines commonly have a primer, which is used to supply fuel from the carburetor to the engine prior to starting the engine, and a bowl drain which is a valve or tube used to drain the fuel from the carburetor bowl. The bowl drain is independent or separate from the primer and is required to drain the bowl of fuel for shipping, maintenance, and engine storage purposes. Two common primer types are a liquid fuel primer and an air pressure primer. The liquid fuel primer injects or pumps a quantity of liquid fuel from the carburetor bowl into the engine intake manifold. The air pressure primer pumps a quantity of air into the space existing above the level of fuel within the carburetor bowl. This air momentarily pressurizes the air space thus forcing some of the liquid fuel from the bowl through the carburetor main nozzle and into the engine intake manifold.
The liquid fuel primer is more expensive than the air pressure primer however it is preferable for larger engines, cold weather applications, and more experienced operators. Directly injecting liquid fuel requires less actuations of the priming bulb for a given quantity of fuel than the air primer. Also with direct fuel injection, the fuel can be placed more accurately into a given area of the carburetor or engine intake. The less expensive air pressure primer has a greater margin of error on the number of depressions or primes, but it still works well on small engines used primarily in warm weather, such as a walk behind lawn mower.
One common type of bowl drain has a fitting normally attached near the top of the carburetor that is connected to a tube extending to the bottom of the carburetor bowl and is normally used by the engine or equipment manufacturer to evacuate the fuel from the bowl of the carburetor after initial testing of the engine at the factory prior to shipment. This is accomplished by putting a suction hose on the fitting and drawing the fuel from the bowl. The fitting is then sealed to prevent contaminants from entering the bowl. This type of bowl drain is ideal for a manufacturing environment having an adequate suction source, because the bowl can be drained in a few seconds as opposed to the much slower gravity drain. Unfortunately, this type of tube bowl drain is of little use to the end user for draining the bowl since the end user seldom has the right size hose and a vacuum source suitable for drawing gasoline from the bowl. A second typical bowl drain has a manually operated valve at or near the bottom of the carburetor bowl which when opened allows the fuel to drain via gravity from the bowl. This second or valve-type of bowl drain is much better suited to the end user of the equipment, but can be inadvertently left open resulting in fuel spill and the inability to start the engine until the valve is manually closed. Moreover, the valve-type of bowl drain requires extra parts leading to higher manufacturing costs.
This invention provides a carburetor with a manual priming pump having an integrated carburetor fuel drain which provides both the engine manufacturer and end user with an easy way to drain fuel from a fuel chamber of the carburetor. The priming pump has a pump chamber defined by a resilient priming bulb. The pump chamber generally communicates between the fuel chamber and a fuel-and-air mixing passage of the carburetor body and is preferably positioned above the fuel chamber. The dual function of the manual priming pump, prime or drain, is switched by a valve with a rotating member engaged sealably between a seat and the resilient priming bulb of the pump. The member moves between a drain position and a priming position thus enabling draining of the fuel chamber or priming of the carburetor via successive manual depressions of the priming bulb.
The member is preferably a rotating disk having a drain fuel-in orifice and a drain fuel-out orifice which when the member is in the drain position align respectively to a fuel draw passage and a fuel drain passage both preferably defined in-part by the carburetor body. The fuel draw passage communicates with the fuel chamber and the fuel drain passage communicates with the environment external to the carburetor. Both passages communicate with the pump chamber when the member is in the drain position, but only the fuel draw passage communicates with the pump chamber when the member is in the priming position. The priming pump may be of either the liquid fuel direct injection or the air pressure type. Either type can be mounted directly on the carburetor body or remotely, such as on an air filter or an engine housing.
Objects, features and advantages of this invention include providing a carburetor priming pump which is also capable of draining the carburetor fuel bowl. The novel priming pump simplifies draining of the fuel bowl for the end user. The invention provides an extremely compact construction and arrangement, a relatively simple design, extremely low cost when mass produced and is rugged, durable, reliable, requires little to no maintenance and in service has a long useful life.